1. Field of the Invention
This invention relates to an ESD (Electrostatic Discharge) protection device.
2. Background Art
Conventionally, an ESD protection diode having a built-in EMI filter for filtering high-frequency signals is formed by inserting ESD protection diodes in parallel between the signal line and the ground electrode and inserting a resistor between the cathodes of the diodes. However, one-chip configuration of a conventional high-pass filter for filtering low-frequency signals has not been achieved. Conventionally, such a high-pass filter is configured by mounting electronic parts of diodes and resistors on a mounting board such as a printed circuit board.
As a conventional technique, JP 11-168175A discloses a surge protection structure connected between two input terminals and two output terminals, the output terminals being connected to the inputs of a circuit to be protected. The first input terminal is connected to the first output terminal via an impedance (which forms a junction capacitance with polysilicon). The second input terminal is connected to the second output terminal. The input terminals are interconnected by a first Zener diode. The output terminals are interconnected by a second Zener diode having the same polarity as the first Zener diode. On the other hand, JP 2002-094012A discloses a protective element where a P+-type polycrystalline Si member is wired on an arbitrary signal transfer path from an input terminal via an input buffer to an internal logic circuit. A P+-type region, an N−-type region, a p−-type region, and an N+-type region are laterally arranged. The N+-type region is connected to an N+-type polycrystalline Si member that is electrically connected to the reference potential (GND). Thus the element forms a thyristor to be triggered by punch-through.